Question

You know that Gip1 is only expressed in adult liver cells and not in the liver of embryos. You also know that Jk8 and Pa5 behave similarly on other promoters in the embryo or in the adult, in terms of whether they act as repressors or gene activators. Given the data, use of which of the following mechanisms would make the most sense for regulating the Jk8 and Pa5 proteins:

(a) Jk8 is ubiquitylated and targeted for destruction in adult cells.
(b) Jk8, but not Pa5, is transcribed in embryonic liver cells.
(c) Jk8 binds to the promoter of the gene that encodes Jk8 in embryonic liver cells.
(d) Pa5 binds to the promoter of the gene that encodes Jk8 in embryonic liver cells.

Answer 1

Ubiquitylation leading to the degradation of Jk8 in adult cells (option a) offers a plausible mechanism that aligns with Gip1 expression patterns in adult liver cells and its absence in embryonic liver, representing a key aspect of differential gene expression and its impact on cellular metabolism.

Step-by-step explanation:

Given that Gip1 is expressed only in adult liver cells and not in the liver of embryos, and the known behavior of Jk8 and Pa5, regulating the activity of these proteins is crucial for controlling gene expression precisely. For Jk8 and Pa5 to behave as required, protein ubiquitylation could be the mechanism at play. In option (a), Jk8 is targeted for destruction in adult cells through ubiquitylation, which is a plausible mechanism since Gip1 is not expressed in embryos. Ubiquitylation often tags proteins for degradation, removing them from the cellular environment when their function is not needed, such as during embryonic stages for Gip1. Meanwhile, options (b), (c), and (d) focus on transcription in embryonic liver cells but do not account for the lack of Gip1 expression in embryos as ubiquitylation does.

Such molecular mechanisms are foundational in the differential gene expression seen in different tissues and developmental stages, which relies on the precise modulation of transcription factors and regulatory proteins. The increase in cellular metabolism in adult liver cells could be associated with the expression of Gip1, necessitating the degradation of repressors like Jk8 to allow adult liver-specific gene expression.